The practice of coating an implantable medical device, such as a stent, with a synthetic or biological active or inactive agent is known. Numerous processes have been proposed for the application of such a coating, for example: soaking or dipping the implantable device in a bath of liquid medication; soaking the device in an agitated bath; and spraying the medication on to the device by way of pressurized nozzles.
Initially, such coatings were applied at the time of manufacture of the medical device. The short shelf life of some drugs, combined with the time span from manufacture to implantation, and the last minute dosage decision concerning a specific drug to be used based on a patient's condition at the time of implantation, have contributed to a need for technologies that permit applying a coating just prior to implantation. These “just in time” approaches include: wrapping the implantable device with medicated conformal film; dipping or soaking in a medicated bath just prior to implantation; and providing a bathing chamber for use with a specific implantable device such as a stent deployed on the balloon of a catheter.
Each of the methods and devices intended for use just prior to implantation, listed above, however, deposits the coating material onto any and all surfaces that are exposed to the coating. This may result in depositing coating material on surfaces on which the coating is unwanted or undesirable. Further, the coating may crack or break away when the implantable device is removed from the implantation apparatus. This cracking may occur on a stent deployed on a catheter balloon. As the balloon is inflated, and the stent is expanded into position, the coating may crack along the interface between the stent and the balloon. These cracks may lead to a breaking away of a portion of the coating from the stent itself. Similar problems can occur in cases where the coating technique fails to prevent inadvertent overlapping with the internal surfaces along the edges of various devices, e.g., struts of stents. This, in turn, may affect the medicinal effectiveness of the coating, and negatively affect the entire medical procedure.
It is known to use ink-jet technology to apply a liquid to selected portions of a surface. In one instance, the selective application of the material is based on an objective predetermined location for deposit rather that on a “subjective placement” as needed to meet the requirements of a specific application procedure. With regard to the application of coatings applied to medical devices with inkjet applicators, it is possible to coat only a chosen portion of a device, such as only the stent mounted on a catheter, but not the catheter itself. This type of procedure using current technologies may, however, require, for example, providing complex data files, such as a CAD image of the device to be coated, and insuring that the device is installed in the coating apparatus in a precise manner so as to be oriented exactly the same as the CAD image.
Alternatively, a real-time picture can be taken with a camera to determine the position of the ink-jet nozzle in relation to the prosthesis. Based upon the feedback of nozzle location, the ink-jet applicator can be controlled by activating the spray, moving the ink-jet nozzle, and/or moving the prosthesis to adjust to the pattern to better conform with the actual prosthesis.
To apply a coating to a stent, it is necessary to distinguish the stent from any surface upon it which might be mounted, e.g., a mandrel or a balloon catheter, and account for configurations that might not be predicted from information such as CAD drawings. Further, it is necessary to distinguish between the struts of the stent and the interstitial spaces so as not to apply coating in the spaces. Being able to distinguish between the spaces and the struts reduces the amount of “wasted” coating material as well as prevents, in the case of a balloon-mounted stent, placing coating material on the balloon surface.